Research Activities
Performance decreases
Loss of righting reflex
Using Intraspecific Variation in Distributional Patterns on an Amphibian Model: Thermal Tolerance and Species Distribution Modeling
Theoretical frameworks, such as niche-based species distribution models (SDMs), have been extensively used to determine how the distributions of species may shift in response to climate change. However, traditional SDMs often assume that the climate niche does not change between populations, and they ignore the relevant trait variation (e.g., thermal tolerance) among populations across a species range.
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I am currently using green treefrogs as a model organism to assess population-level variation in thermal tolerance (CTmin, CTmax) in their expanded and historical range. I am also in the process of incorporating the variation found in thermal tolerance into an SDM to see if this mechanistic approach improves prediction accuracy.
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Does Dispersal Explain the Range Expansion of the Green Treefrog (Hyla cinerea)?
The globe is warming and species are changing their geographic distributions. A typical response to these warming patterns is for species to migrate towards higher elevations and latitudes to track more suitable thermal conditions. Since the 1980s, green treefrogs have been undergoing a rapid and ongoing hypothesized climate-related range expansion moving northeast bound into the states of Indiana, Kentucky, and Illinois.
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Since anuran leg-length is correlated with locomotor function, longer legs have been shown to facilitate dispersal of invasive anuran populations undergoing biological invasion.
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We tested if if green treefrogs on the front end of their expansion exhibited similar changes in dispersal-related traits as those found in invasive species. We found that relative to snout-vent-length, the femur lengths of these frogs from their expanded-range were significantly larger than those found in their historical range. These results suggest that native expanded-range populations of this species have undergone changes in morphology related to dispersal.
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Conclusion:
1. Native expanded-range populations of these frogs have undergone changes in morphology that may be related to pressures for dispersal.
2. These rapid shifts in morphology appear to mimic morphological trade-offs observed in invasive species of anurans.
Does Parasitic Escape Facilitate the Range Expansion of the Green Treefrog (Hyla cinerea)?
Parasites are ubiquitous in ecological communities and are well known to impose powerful selective pressures on their hosts. Specifically in species' range expansions, significant reductions of prevalence and intensity of parasitic infections (i.e., parasitic escape) have been observed in host populations.
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By definition, there are lower population densities on a species' expanding edge. Therefore, reduced parasitism may be directly related to serial founder events as well as lower transmission rates directly due to lower host density.
A recent study has found significant reductions of helminth diversity in expanded range green treefrogs compared to those found in their historical range suggesting parasitic escape to be a factor that may be aiding in their expansion.
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However, more recently, we have found that these results do not hold true in the state of Illinois where many of these frogs have expanded into new counties in the last 5 years. These results downplay the role of parasitic escape occurring with the green treefrog range expansion.
Conclusion:
The patterns of helminth structure in expanded range green treefrogs may instead be primarily influenced by other interactions (e.g., host density, host diversity, interspecific parasitic interactions, and temperature/precipitation).
